In so-called superconducting machines at least one superconducting winding is provided, with so-called high temperature superconductors (HTS superconductors) frequently being used. HTS superconductor refers to metal oxide superconductor materials with transition temperatures tc above 77K.
Cryogenic liquids are generally used as the coolant to cool superconductors, in particular also in superconducting machines. Thus for example cooling devices for HTS superconductors are known, in which for example a coolant in the form of neon gas or nitrogen is liquefied at a cold head with a condenser in a closed system. From there the coolant flows out into the part supporting the superconductor, for example a rotor to be cooled. The evaporating coolant returns to the condenser and is liquefied again there. The so-called thermosiphon effect is utilized in this process. The liquid coolant evaporates at a heat conducting support, which supports the superconductor, in particular a winding support, and flows back to the condenser in a gaseous form due to the pressure difference resulting from the evaporation in the evaporator and the condensing in the condenser chamber of the condenser. Such coolant flows are also referred to as heat pipes.
The liquid coolant is transported to the superconductor by gravity with known cooling devices. This means that the condenser is disposed geodetically higher than the evaporator. A closed cooling system is generally formed.
This procedure always proves problematic, when an oblique position of the cooling device or the synchronous machine containing it can occur, as is possible for example with superconducting synchronous machines for use on ships, in other words for example HTS motors or HTS generators. With vessels such as ships an oblique position or inclination of the ship can easily occur. Such static slanting positions are referred to as trim but dynamic slanting positions are also possible. In some instances the liquid coolant may then not be able to reach the evaporator and its cooling action will fail.
To resolve this problem it has been proposed that whenever inclination of the cooling device and in particular therefore also the coolant line may occur, the geodetic height of the liquid level is used or the entire superconducting machine is installed already inclined. This means in particular that the condenser with the cold head is disposed much higher than the superconductor to be cooled. If there is enough liquid coolant in the closed system and the liquid level is therefore high enough, the liquid coolant can be conveyed to the superconductor, in particular into the rotor, despite a rising coolant line.
This procedure has the disadvantage that a large quantity of liquid coolant has to be maintained in the system. There are also restrictions in respect of the arrangement of the different components and the course of the coolant lines, which affects the design of the cooling device.
These design restrictions are also present in other areas of application, when there is little space, meaning that a geodetically higher condenser with a cold head, which is generally connected to a refrigeration unit, cannot be provided. This applies in particular in the case of height restrictions for a device, for example a rail motor unit or the like.
The use of mechanical devices such as pumps requires a large outlay in respect of equipment and energy, which increases further for low coolant temperatures.